Photoelectron source, multi-photoelectron source, and multi-beam irradiation apparatus

Abstract

To provide a photoelectron source that uses excitation light efficiently and allows multi-beam formation with ease.SOLUTION: The photoelectron source according to one embodiment of the present invention includes: a photoelectric surface supported on a surface of a substrate; a light source for irradiating excitation light from the back surface side of the substrate; an electrode disposed at a position facing the photoelectric surface on the surface side of the substrate and applying an electric field in the direction of extracting electrons from the photoelectric surface; an extraction hole through which photoelectrons extracted from the photoelectric surface pass; and a reflector for reflecting the excitation light having passed through the substrate to irradiate the photoelectric surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a photoelectron source, a multi-photoelectron source, and a multi-beam irradiation device. [Background technology]

[0002] In recent years, with the increasing integration density of LSIs, the circuit line width required for semiconductor devices has become finer year by year. Here, electron beam (EB) lithography technology has inherently excellent resolution, and mask patterns are written onto mask blanks using an electron beam.

[0003] For example, there is a lithography system that uses multiple beams. Compared to lithography using a single electron beam, using multiple beams allows for the irradiation of many beams at once, greatly improving throughput. In a multi-beam lithography system, for example, an electron beam emitted from an electron gun is passed through a mask with multiple holes to form multiple beams, each of which is blanked and each beam that is not blocked by the limiting aperture is reduced in size by the optical system, the mask image is reduced, and the beam is deflected by a deflector to be irradiated onto the desired position on the sample.

[0004] As an electron beam source, a technology is being considered in which the back surface (top surface) of a photocathode is irradiated with excitation light and electrons are emitted from the front surface (bottom surface) to form an electron beam. In this case, the excitation light needs to be thin enough to reach the surface of the photocathode, which poses a problem of low utilization efficiency of the excitation light.

[0005] A configuration has also been proposed in which excitation light is irradiated onto the surface of the photocathode and an electron beam is emitted from the surface of the photocathode, but with a method in which excitation light is irradiated onto the surface of the photocathode, it is difficult to achieve multi-beam generation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 129826 / 1983 [Patent Document 2] Japanese Patent Application Publication No. 60-014245 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-204404 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a photoelectron source that efficiently uses excitation light and can easily produce multiple beams, and a multi-photoelectron source and multi-beam irradiation device that include a plurality of photoelectron sources. [Means for solving the problem]

[0008] A photoelectron source according to one aspect of the present invention comprises a photocathode supported on the surface of a substrate, a light source that introduces excitation light from the back side of the substrate, an electrode that is positioned on the surface side of the substrate facing the photocathode and applies an electric field to the photocathode in a direction that extracts electrons, and a reflector that has an extraction hole formed therein through which photoelectrons extracted from the photocathode pass and that reflects the excitation light that has passed through the substrate and irradiates it onto the photocathode.

[0009] A multi-photoelectron source according to one aspect of the present invention includes a plurality of the photoelectron sources described above, and generates a multi-electron beam by photoelectrons extracted from the extraction holes of the plurality of photoelectron sources, respectively.

[0010] A multi-beam irradiation device according to one aspect of the present invention includes the above-described multi-photoelectron source, and a stage on which a substrate to be irradiated with the multi-electron beams generated by the multi-photoelectron source is placed. [Effects of the Invention]

[0011] According to the photoelectron source of the present invention, the excitation light can be used efficiently and multiple beams can be easily generated. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram illustrating the configuration of a photoelectron source according to an embodiment of the present invention. [Figure 2] FIG. 10 is a schematic diagram illustrating the configuration of a photoelectron source according to another embodiment. [Figure 3] FIG. [Figure 4] FIG. 10 is a schematic diagram illustrating the configuration of a photoelectron source according to another embodiment. [Figure 5] FIG. 10 is a schematic diagram illustrating the configuration of a photoelectron source according to another embodiment. [Figure 6] FIG. 1 is a schematic diagram illustrating the configuration of a multi-photoelectron source. [Figure 7] FIG. 10 is a schematic diagram illustrating the configuration of a multi-photoelectron source according to a modified example. [Figure 8] FIG. 1 is a schematic diagram illustrating the configuration of a multi-beam drawing apparatus. [Figure 9] FIG. 1 is a schematic diagram illustrating the configuration of a multi-beam inspection device. [Figure 10] FIG. 10 is a schematic configuration diagram of a photoelectron source according to a modified example. [Figure 11] FIG. 10 is a schematic configuration diagram of a photoelectron source according to a modified example. [Figure 12] FIG. 10 is a schematic configuration diagram of a photoelectron source according to a modified example. [Figure 13] FIG. 10 is a diagram illustrating an example of an arrangement of optical fibers. [Figure 14] FIG. 10 is a schematic configuration diagram of a photoelectron source according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0014] As shown in FIG. 1, the photoelectron source according to this embodiment includes a glass substrate 1, a conductive film 2 formed on one surface of the glass substrate 1, a photocathode 3 provided on the conductive film 2, a focusing mirror 4 (reflector), a light source 5, and a lens 6. In this embodiment, the lower surfaces of the glass substrate 1, the conductive film 2, and the photocathode 3 in FIG. 1 are referred to as the back surfaces, and the upper surfaces are referred to as the front surfaces. That is, the conductive film 2 is formed on the front surface of the glass substrate 1. The photocathode 3 is formed on the front surface of the conductive film 2. The back surface of the photocathode 3 is in contact with the front surface of the conductive film 2.

[0015] The focusing mirror 4 is disposed on the front surface side of the glass substrate 1 at a position facing the photocathode 3. The light source 5 and the lens 6 are disposed on the rear surface side of the glass substrate 1.

[0016] The glass substrate 1 is a substrate that allows excitation light to pass through, and is made of synthetic quartz or sapphire glass. The glass substrate 1 is used, for example, as a partition window that separates a vacuum space from a non-vacuum space while allowing light to pass through. Including the example in Figure 1, the surface of the glass material through which the excitation light passes is coated with an anti-reflection film against the excitation light, if necessary.

[0017] The conductive film 2 has an antistatic function, is transparent, and allows excitation light to pass through. The conductive film 2 may be, for example, a SnGeO film.

[0018] When excitation light is incident on the photocathode 3, it emits photoelectrons. Materials that can be used for the photocathode 3 include gold, diamond, LaB6, low work function metals, and semiconductors such as GaN. The thickness of the photocathode 3 is sufficiently thicker than the penetration depth of the excitation light, for example, about 1 μm.

[0019] The light source 5 generates laser light (excitation light). For example, the light source 5 generates ultraviolet light with a wavelength of about 260 to 280 nm as the laser light. The light source 5 is not limited to a laser light source, and may be other light sources such as an LED or a lamp. The light source 5 may include a beam expander or the like.

[0020] The lens 6 is, for example, a convex lens. The laser light generated by the light source 5 is incident on the lens 6, refracted, travels parallel to the optical axis, passes through the glass substrate 1 and the conductive film 2, and is incident on the focusing mirror 4.

[0021] The focusing mirror 4 is a concave mirror that reflects the incident laser light (parallel light beam) so as to focus it on the surface of the photocathode 3. For example, the focusing mirror 4 can be a silicon substrate whose laser light reflecting surface is coated with aluminum, rhodium, or ruthenium.

[0022] A potential that is positive relative to the photocathode 3 is applied to the focusing mirror 4 from a power supply (not shown), and the focusing mirror 4 functions as an extraction electrode for photoelectrons. Also, an extraction hole H1 through which photoelectrons pass is formed in the focusing mirror 4.

[0023] Photocathode 3 generates photoelectrons when laser light reflected from focusing mirror 4 is incident on it. The generated photoelectrons are extracted from the surface of photocathode 3 toward focusing mirror 4 by a positive potential applied to focusing mirror 4. These photoelectrons pass through extraction hole H1 in focusing mirror 4, and electron beam B is emitted.

[0024] In this photoelectron source, excitation light is incident on the surface of the photocathode 3 and photoelectrons are extracted from the surface, eliminating the need to thin the photocathode 3 and enabling efficient use of the excitation light. Furthermore, the excitation light is condensed after passing through the glass substrate, which can suppress the decrease in excitation light transmittance that occurs with the generation of defects when high-intensity ultraviolet light is irradiated onto a glass substrate. In addition, because the excitation light irradiation mechanism (light source 5 and lens 6) is located on the back side of the photocathode 3, it is easier to achieve multi-beam generation compared to when it is located on the front side.

[0025] Fig. 2 is a schematic diagram of a photoelectron source according to another embodiment. The same components as those in the embodiment shown in Fig. 1 are assigned the same reference numerals, and descriptions thereof will be omitted. In the photoelectron source shown in Fig. 2, the conductive film 2 is omitted from the photoelectron source shown in Fig. 1, and a support plate 7 is arranged on the front surface of a glass substrate 1 at a distance from the glass substrate 1, and a photocathode 3 is formed on the surface of the support plate 7.

[0026] The support plate 7 is a light-shielding plate, and is made of, for example, a silicon substrate. An opening 7a through which laser light passes is formed in the support plate 7 in an area other than the installation location 7b of the photocathode 3. For example, as shown in FIG. 3, the opening 7a is formed so as to surround the installation location 7b of the photocathode 3, and a structural portion 7c on the outer periphery side of the opening 7a and the installation location 7b of the photocathode 3 are connected by a plurality of beams 7d, thereby supporting the installation location 7b. In the example of FIG. 3, four beams 7d are provided, which are arranged symmetrically (at 90° intervals).

[0027] The laser light emitted from the light source 5 is refracted by the lens 6 to become light parallel to the optical axis, passes through the glass substrate 1, passes through the opening 7a in the support plate 7, and is incident on the focusing mirror 4. The laser light reflected from the focusing mirror 4 is focused and incident on the photocathode 3, and the generated photoelectrons pass through the extraction hole H1 in the focusing mirror 4, and an electron beam B is emitted.

[0028] 1, this photoelectron source also receives excitation light from the surface of the photocathode 3 and photoelectrons are extracted from the surface, which eliminates the need to thin the photocathode 3 and allows for efficient use of excitation light. In addition, the excitation light irradiation mechanism (light source 5 and lens 6) is located on the back side of the photocathode 3, making it easy to achieve multi-beam generation.

[0029] Fig. 4 is a schematic diagram of a photoelectron source according to another embodiment. The same parts as those in the embodiment shown in Fig. 1 are given the same reference numerals, and descriptions thereof will be omitted. The photoelectron source shown in Fig. 4 differs from the photoelectron source shown in Fig. 1 in that a reflecting mirror 9, which is a plane mirror, is installed instead of the focusing mirror 4, and a light-shielding film 8 is formed on the rear surface of the glass substrate 1.

[0030] The reflecting mirror 9 can be a silicon substrate whose laser light reflecting surface (rear surface) is coated with aluminum, rhodium, or ruthenium.

[0031] A potential that is positive relative to the photocathode 3 is applied to the reflector 9 from a power source (not shown), and the reflector 9 functions as an extraction electrode for photoelectrons. Also, an extraction hole H2 through which photoelectrons pass is formed in the reflector 9.

[0032] The light-shielding film 8 is, for example, a chromium film. An opening 8a for passing laser light is formed in the light-shielding film 8. The opening 8a is formed so that the laser light from the light source 5 does not reach the extraction hole H2 of the reflecting mirror 9 (does not pass through the extraction hole H2).

[0033] Laser light emitted from light source 5 is refracted by lens 6 to become focused light, passes through opening 8a in light-shielding film 8, transmits through glass substrate 1 and conductive film 2, is reflected by reflecting mirror 9, and is focused and incident on the surface of photocathode 3. Photoelectrons generated by the laser light incident on photocathode 3 pass through extraction hole H2 in reflecting mirror 9, and electron beam B is emitted.

[0034] 1, this photoelectron source also receives excitation light from the surface of the photocathode 3 and photoelectrons are extracted from the surface, eliminating the need to thin the photocathode 3 and allowing for efficient use of the excitation light. Furthermore, the excitation light irradiation mechanism (light source 5 and lens 6) is located on the back side of the photocathode 3, making it easy to achieve multi-beam generation. Furthermore, because the reflecting mirror 9 is a plane mirror, it is easier to manufacture than when a concave mirror is used.

[0035] 4, the laser light is refracted by lens 6, but as shown in Fig. 11, a converging mirror set consisting of a convex mirror 16 and a concave mirror 18 may be used instead of lens 6. The laser light generated from light source 5 is reflected by convex mirror 16 to spread, and is reflected by concave mirror 18 to become a convergent light, which passes through opening 8a in light-shielding film 8.

[0036] Fig. 5 is a schematic diagram of a photoelectron source according to another embodiment. Components similar to those in the embodiment shown in Fig. 2 are given the same reference numerals and descriptions thereof will be omitted. The photoelectron source shown in Fig. 5 differs from the photoelectron source shown in Fig. 2 in that a reflecting mirror 9, which is a plane mirror, is installed instead of the focusing mirror 4.

[0037] The reflecting mirror 9 can be a silicon substrate whose laser light reflecting surface (rear surface) is coated with aluminum, rhodium, or ruthenium.

[0038] A potential that is positive relative to the photocathode 3 is applied to the reflector 9 from a power source (not shown), and the reflector 9 functions as an extraction electrode for photoelectrons. Also, an extraction hole H2 through which photoelectrons pass is formed in the reflector 9.

[0039] The opening 7a of the support plate 7 is formed so that the laser light from the light source 5 does not reach the extraction hole H2 of the reflecting mirror 9.

[0040] The laser light emitted from the light source 5 is refracted by the lens 6 to become a focused light, which passes through the glass substrate 1, passes through the opening 7a in the support plate 7, is reflected by the reflecting mirror 9, and is focused and incident on the surface of the photocathode 3. Photoelectrons generated by the laser light incident on the photocathode 3 pass through the extraction hole H2 in the reflecting mirror 9, and an electron beam B is emitted.

[0041] In the configuration shown in FIG. 5, instead of the lens 6, a light-collecting mirror set (see FIG. 11) in which a convex mirror 16 and a concave mirror 18 are combined can be used.

[0042] 2, this photoelectron source also receives excitation light from the surface of the photocathode 3 and photoelectrons are extracted from the surface, eliminating the need to thin the photocathode 3 and allowing for efficient use of the excitation light. Furthermore, the excitation light irradiation mechanism (light source 5 and lens 6) is located on the back side of the photocathode 3, making it easy to achieve multi-beam generation. Furthermore, because the reflecting mirror 9 is a plane mirror, it is easier to manufacture than when a concave mirror is used.

[0043] FIG. 6 is a schematic diagram of a multi-photoelectron source that generates multiple beams using a plurality of photoelectron sources shown in FIG.

[0044] The multi-photoelectron source has a light source array 5A, a lens array 6A, a glass substrate 1, a conductive film 2, a photocathode 3, a light-shielding film 8, a reflector array 9A, and an angle-limiting aperture array substrate 10. The glass substrate 1, the reflector array 9A, and the angle-limiting aperture array substrate 10 are held by a peripheral wall portion 12.

[0045] The light source array 5A has a plurality of light sources 5 arranged in an array, and may be, for example, an LED array. The on / off light emission of each of the plurality of light sources of the light source array 5A is controlled by a light emission control circuit 11. Alternatively, a laser diode (LD) array may be used as the light source array 5A.

[0046] The lens array 6A has a plurality of lenses 6 corresponding to the plurality of light sources 5 of the light source array 5A. The reflector array 9A has a plurality of reflectors 9 corresponding to the plurality of light sources 5 of the light source array 5A.

[0047] The angle-limiting aperture array substrate 10 is disposed downstream of the reflecting mirror array 9A in the beam traveling direction. A plurality of apertures (openings) are formed on the angle-limiting aperture array substrate 10 to limit the divergence angle of the electron beams emitted from the extraction holes of the reflecting mirrors 9 of the reflecting mirror array 9A. Tantalum, for example, can be used as a material for the angle-limiting aperture array substrate 10.

[0048] That is, a lens 6, a photocathode 3, a reflecting mirror 9, and an angle limiting aperture are provided so as to correspond to each light source 5 of the light source array 5A.

[0049] The excitation light emitted from the light source 5 of the light source array 5A is refracted by the corresponding lens 6 of the lens array 6A to become focused light, passes through the opening in the light-shielding film 8, transmits through the glass substrate 1 and the conductive film 2, is reflected by the reflecting mirror 9, and is focused and incident on the surface of the photocathode 3. Photoelectrons generated by the laser light incident on the photocathode 3 pass through the extraction hole in the reflecting mirror 9, and an electron beam B is emitted.

[0050] The beam divergence angle of the electron beam B is limited by the angle-limiting aperture array substrate 10. This suppresses electrons emitted at large angles and makes the emission angle between beams uniform, thereby suppressing variations in the blur of the beam (the focused light source image) due to aberrations in the downstream lens system.

[0051] By emitting electron beams B from multiple photocathode 3, multiple beams can be formed. Furthermore, the current distribution of the multiple beams can be controlled by controlling the light emission intensity of each light source using light emission control circuit 11. For example, when the photoelectron generation efficiency of each photocathode that generates each beam of the multiple beams is not equal, the current of each beam can be controlled to be the same by controlling the light emission intensity. Conversely, the distribution of light emission intensity can also be controlled to obtain a desired current distribution.

[0052] An opening E for evacuation may be provided in the peripheral wall 12 between the reflecting mirror array 9A and the angle-limiting aperture array substrate 10, or in a position sufficiently distant from the aperture of the angle-limiting aperture array substrate 10.

[0053] In the multi-photoelectron source, excitation light may be guided to each lens of the lens array 6A via an optical fiber bundle 60 in which a plurality of optical fibers 62 are bundled, as shown in FIG.

[0054] Although a multi-photoelectron source using a plurality of photoelectron sources shown in FIG. 4 has been described in FIG. 6, a multi-photoelectron source using a plurality of photoelectron sources shown in FIG. 1, FIG. 2 or FIG. 5 may also be used.

[0055] The multi-photoelectron source can be applied to a multi-beam irradiation device such as a multi-beam drawing device or a multi-beam inspection device.

[0056] 8 shows an example of the configuration of a multi-beam lithography system. The multi-beam lithography system has a lens barrel 50 and a lithography chamber 51, and the interior of the lens barrel 50 and the lithography chamber 51 are evacuated by a vacuum pump (not shown).

[0057] Arranged within the lens barrel 50 are an acceleration / focusing block 20, multiple stages of electromagnetic lenses 23 and 24, a deflector 25, etc. Arranged within the acceleration / focusing block 20 are a multi-photoelectron source 21 and an acceleration electrode group 22.

[0058] An XY stage 26 is arranged in the patterning chamber 51, and a sample 27, such as a mask blank coated with resist and serving as a substrate to be patterned, is placed on the XY stage 26. The XY stage 26 is movable in the X and Y directions by a drive mechanism 28.

[0059] The multi-photoelectron source 21 has the same configuration as the multi-photoelectron source shown in Fig. 6. The light source array 5A and the lens array 6A shown in Fig. 6 are disposed outside the vacuum lens barrel 50.

[0060] The multi-beams emitted from the multi-photoelectron source 21 are accelerated by the accelerating electrode group 22 and focused on the sample surface as a pattern image with the desired reduction ratio by electromagnetic lenses 23 and 24. The dashed lines in the figure indicate the on-axis trajectory K1 and the off-axis trajectory K2. The entire multi-beam is deflected in the same direction by the deflector 25, and each beam is irradiated onto its respective irradiation position on the sample 27. When the XY stage 26 is moving continuously, the deflector 25 controls the beam irradiation position so that it follows the movement of the XY stage 26.

[0061] When a desired pattern is drawn on the sample 27, the light emission control circuit 11 (see FIG. 6) controls the light sources corresponding to unnecessary beams to turn off their light emissions.

[0062] 9 shows an example of the configuration of a multi-beam inspection device. The multi-beam inspection device has a lens barrel 52 and an inspection chamber 53, and the interior of the lens barrel 52 and the inspection chamber 53 are evacuated by a vacuum pump (not shown).

[0063] Arranged within the lens barrel 52 are an acceleration-focusing block 30, multiple stages of electromagnetic lenses 33 and 34, a deflector 35, a beam separator 41, a deflector 42, projection lenses 43 and 44, a multi-detector 45, etc. Arranged within the acceleration-focusing block 30 are a multi-photoelectron source 31 and an acceleration electrode group 32.

[0064] An XY stage 36 is placed in the inspection chamber 53, and a substrate 40 to be inspected is placed on the XY stage 36. The substrate 40 may be a semiconductor substrate, a chip on which a pattern is formed, a mask for forming a pattern, or the like. The XY stage 36 can be moved in the X and Y directions by a drive mechanism 38.

[0065] The multi-photoelectron source 31 has the same configuration as the multi-photoelectron source shown in Fig. 6. The light source array 5A and the lens array 6A shown in Fig. 6 are disposed outside the vacuum lens barrel 52.

[0066] The multiple beams (multiple primary electron beams) emitted from the multiple photoelectron source 31 are accelerated by the accelerating electrode group 32 and are focused on the substrate 40 as a pattern image with a desired reduction ratio by the electromagnetic lenses 33 and 34. The multiple beams are all deflected in the same direction by the deflector 35, and each beam is irradiated onto its respective irradiation position on the substrate 40. When the XY stage 36 is moving continuously, the deflector 35 controls the irradiation position of the beam so that it follows the movement of the XY stage 36 (tracking deflection).

[0067] A retarding voltage is applied to the substrate 40 by a deceleration voltage supply power supply 39 , and the multiple primary electron beams are decelerated just before the substrate 40 .

[0068] As a result of the multiple primary electron beams being irradiated onto the desired positions of the substrate 40, a bundle of secondary electrons (multiple secondary electron beams) including reflected electrons corresponding to each beam of the multiple primary electron beams is emitted from the substrate 40.

[0069] The multiple secondary electron beams emitted from the substrate 40 proceed to the beam separator 41. The beam separator 41 generates an electric field and a magnetic field in orthogonal directions on a plane orthogonal to the direction (optical axis) in which the multiple primary electron beams proceed. The electric field exerts a force in the same direction regardless of the electron's direction of travel. In contrast, the magnetic field exerts a force according to Fleming's left-hand rule. Therefore, the direction of the force acting on the electrons can be changed depending on the direction in which the electrons enter. For the multiple primary electron beams entering the beam separator 41 from above, the forces due to the electric field and the magnetic field cancel each other out, causing the multiple primary electron beams to proceed straight downward. In contrast, for the multiple secondary electron beams entering the beam separator 41 from below, the forces due to the electric field and the magnetic field act in the same direction, causing the multiple secondary electron beams to bend diagonally upward.

[0070] The multiple secondary electron beams bent obliquely upward are refracted by projection lenses 43 and 44 and projected onto the multi-detector 45. The multi-detector 45 detects the projected multiple secondary electron beams. The multi-detector 45 has multiple detection pixels. The multi-detector 45 has, for example, a diode-type two-dimensional sensor (not shown). Then, at the diode-type two-dimensional sensor positions corresponding to each beam of the multiple secondary electron beams, each secondary electron of the multiple secondary electron beams collides with the diode-type two-dimensional sensor, generating secondary electron image data for each pixel. In addition, since scanning is performed while the XY stage 36 is continuously moved, tracking deflection is performed as described above. In accordance with the movement of the deflection position due to tracking deflection, the deflector 42 deflects the multiple secondary electron beams so that they are irradiated at desired positions on the light-receiving surface of the multi-detector 45.

[0071] The detection data (measurement image) of the secondary electrons detected by the multi-detector 45 is compared with a reference image based on the design pattern data to determine whether or not there is a defect.

[0072] In the above embodiment, a cleaning gas may be introduced or a heating mechanism may be provided in order to remove contamination from the photocathode 3. The cleaning gas may be, for example, hydrogen gas excited to generate atomic hydrogen.

[0073] FIG. 10 shows a modified photoelectron source. The configuration shown in FIG. 10 differs from the configuration shown in FIG. 1 in that a grid electrode 14 with a high aperture ratio for the excitation light is provided between the focusing mirror 4 and the photocathode 3 and glass substrate 1. Instead of using the focusing mirror 4 as an extraction electrode, the grid electrode 14 is applied with a positive potential relative to the photocathode 3 to extract photoelectrons. In the configuration shown in FIG. 10, the focusing mirror 4 is typically applied with a potential so that it is at a positive potential relative to the photocathode 3. When photoelectrons are not being extracted, the grid electrode 14 is set to the same potential or a negative potential relative to the photocathode 3. In the configuration shown in FIG. 10, the grid electrode 14 partially blocks the excitation light, resulting in a lower utilization efficiency of the excitation light compared to the configuration shown in FIG. 1. However, because the shapes of the grid electrode 14 and the focusing mirror 4 can be determined independently, the respective shapes can be optimized in terms of photoelectron extraction and excitation light collection. Furthermore, since the grid electrode 14 has an electrostatic shielding effect, even if an insulating material is used for the focusing mirror 4 and the surface of the focusing mirror becomes charged, the influence on the extraction of photoelectrons can be suppressed.

[0074] In the above embodiment, a configuration has been described in which excitation light generated from one light source is incident on one photocathode. However, excitation light generated from multiple light sources may be incident on one photocathode, and the intensity of the excitation light incident on the photocathode may be adjusted.

[0075] FIG. 12 shows a configuration in which excitation light that has passed through multiple optical fibers 62 is incident on the photocathode 3 of the photoelectron source shown in FIG. 2. For example, as shown in FIG. 13, excitation light that has passed through four optical fibers 62 supported on a support plate 64 is incident on one photocathode 3. Light sources whose intensity can be controlled independently are connected to each of the four optical fibers 62, and the intensity of the excitation light incident on the photocathode 3 is controlled. By controlling the on / off of each of the light sources connected to the four optical fibers 62, the intensity of the excitation light incident on the photocathode 3 can be controlled in five stages. Furthermore, by adjusting the intensity of each light source, even finer control is possible.

[0076] Fig. 14 shows a configuration in which excitation light from multiple (for example, four) light sources 5 is incident on the photocathode 3 of the photoelectron source shown in Fig. 1. By independently controlling the outputs of the multiple light sources 5, the intensity of the excitation light incident on the photocathode 3 can be adjusted in multiple stages.

[0077] The present invention is not limited to the above-described embodiments, and modifications of the components can be made without departing from the spirit of the invention. For example, instead of controlling the excitation light output, a blanker or blanking array can be provided downstream of the electron source to control whether the electron beam reaches the sample surface, while maintaining a constant excitation light output. This allows for high-speed control of the electron beam's arrival at the sample surface and the distribution of the multi-beams. Instead of applying a constant positive potential to the electrodes, a positive potential can be applied when the beam is extracted, and the same or negative potential can be applied when the beam is not extracted. When controlling the on / off of each beam independently in a multi-beam system, the resistance between adjacent electrodes can be set sufficiently high so that each electrode can be controlled independently. Conversely, the potential of the photocathode relative to the electrode can be controlled to be negative when the beam is extracted. When photoelectrons are not extracted, the same or positive potential can be applied to the electrode. Furthermore, while the photocathode is formed as a film in the above example, a thin film or bulk material can also be used. Various inventions can be realized by appropriately combining the multiple components disclosed in the above embodiments. For example, some components may be omitted from all the components shown in the embodiments.Furthermore, components from different embodiments may be combined as appropriate. [Explanation of symbols]

[0078] 1. Glass substrate 2. Conductive film 3 Photocathode 4 Focusing mirror 5 light source 6 Lenses 7 Support plate 8 Light-shielding film 9 Reflector

Claims

1. a photocathode supported on a surface of a substrate; a light source that emits excitation light from the back side of the substrate; an electrode disposed on the front surface side of the substrate at a position facing the photocathode, the electrode applying an electric field to the photocathode in a direction that extracts electrons; a reflector formed with an extraction hole through which photoelectrons extracted from the photocathode pass, and which reflects the excitation light that has passed through the substrate and irradiates the excitation light onto the photocathode; A photoelectron source comprising:

2. 10. A photoelectron source according to claim 1, wherein a positive potential is applied to the electrodes.

3. 2. The photoelectron source according to claim 1, wherein the electrode has an extraction hole formed therein through which photoelectrons extracted from the photocathode pass, and the electrode is used as the reflecting mirror that reflects the excitation light that has passed through the substrate and irradiates the photocathode.

4. 2. A photoelectron source according to claim 1, wherein said reflecting mirror is a concave mirror that focuses incident excitation light and illuminates said photocathode.

5. 5. A photoelectron source according to claim 4, wherein the concave mirror has a silicon substrate whose light-reflecting surface is coated with aluminum, rhodium or ruthenium.

6. the reflecting mirror is a plane mirror, 2. A photoelectron source according to claim 1, further comprising a lens or a focusing mirror set provided between said light source and said substrate for focusing said excitation light reflected by said plane mirror on said photocathode.

7. The photoelectron source according to claim 1 , wherein the substrate is transparent to the excitation light.

8. a conductive film that is provided on a surface of the substrate and that is transmissive to the excitation light; 8. A photoelectron source according to claim 7, wherein said photocathode is provided on said conductive film.

9. 9. A photoelectron source according to claim 8, wherein the conductive film is a SnGeO film.

10. the substrate is a support plate on which the photocathode is formed, 2. A photoelectron source according to claim 1, wherein an opening through which the excitation light passes is formed in an area of the support plate other than the area where the photocathode is formed.

11. The photoelectron source according to claim 10 , wherein the support plate is a light-shielding plate.

12. a plurality of the light sources; 2. The photoelectron source according to claim 1, wherein one of said photocathode is irradiated with excitation light from said plurality of light sources.

13. The photoelectron source according to claim 12 , wherein the intensity of excitation light from the plurality of light sources is independently controllable.

14. A plurality of photoelectron sources according to claim 1 are provided, a multi-photoelectron source that generates multiple electron beams by photoelectrons extracted from the extraction holes of the plurality of photoelectron sources, respectively;

15. 15. The multi-photoelectron source according to claim 14, further comprising an angle-limiting aperture array substrate on which an aperture corresponding to each of the multiple electron beams is formed, the aperture limiting the divergence angle of the electron beam passing through the aperture.

16. A multi-photoelectron source according to claim 14; a stage for placing a substrate on which the substrate is irradiated with the multiple electron beams generated by the multiple photoelectron source; A multi-beam irradiation device comprising:

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